1. Field of the Invention
The invention relates to a method of welding of work pieces by pulsed laser radiation, in particular of components of precision and micro system technology, in accordance with the preamble of claim 1. The joining of components in the field of horology and, in this context, the welding of clock or watch components such as pinions, crowns and axles of mechanical clocks or watches is a preferred field of application.
A further field of application is the electric industry, for instance in the area of sensors equipped with diaphragms for measuring gas pressures or temperatures. Such sensors require especially thin diaphragms reliably welded to the remaining components.
Furthermore, the invention may be applied in the area of automotive industry, for instance for joining rotationally symmetric components of a diameter less than 5 mm, for instance components of fuel feed devices for combustion engines or for connecting hubs to shafts. Plug connections may be produced as well by the welding method in accordance with the invention, particularly such plugs which have hitherto typically been soldered with a lead-containing solder. Plugs of copper and brass may be produced particularly well. In addition, the invention is particularly well suited for welding foil capacitors in view of the fact that low energy application is required for the protection of the dielectric disposed between the foils which has not heretofore been achievable by conventional resistance gap welding.
The method according to the invention is furthermore suitable for welding together components of different materials such as, in particular, for welding together steel and brass.
2. The Prior Art.
In the field of macro technology, laser beam welding is generally known, and this contexts it constitutes a major field of application of lasers. Thus, DE 3,820,848 A1 discloses a welding method with pulsed laser radiation the intensity of which is controlled for forming at the connection site a laser-induced plasma as a function of one or more connection site parameters.
Furthermore, EP 0,440,002 B1 describes a device for spot welding by which body components of an automotive vehicle are welded by means of a multiple-joint robot arm. In this arrangement, the parts to be welded move by the welding robot arm at low velocity and are welded thereby be a plurality of spot welds.
EP, 0923,424 B1 teaches the use of a movably mounted beam deflection unit with a stationary laser welding head, which by a plurality of spot welds yields a corresponding number of line welds which are spatially separated from each other.
Aside from the selection of pulsed laser radiation for the welding of macro components as in the previously mentioned publications, welding by continuous laser radiation is also known. In general, this results in a more uniform application of energy into the components to be welded and, therefore, to lower distortion. A further advantage resides in the reduced soiling of the components. by liquified or vaporized material.
Furthermore, it is generally known that processing and fabrication methods in the field of macro technology cannot usually be transferred to the field of micro systems technology. Based upon the specific conditions of the micro systems technology, new or specially adapted processes are often required. Because of their small dimensions, components of mechanical watches are typically joined by adhesive or press joining methods, for instance.
The adhesive method requires pre and post processing steps, however, and the components have to b cleaned in a time-consuming manner. Moreover, a further processing steps is necessary, i.e. the application of the adhesive. These requirements significantly prolong the fabrication process. In addition, in respect of the intended adhesive connect ion, the time between application of the adhesive and connection of the parts is critical.
In the case of pressed connections, narrow mechanical tolerances must be maintained which limit the application of press joining technology. The press joining technology requires the application of mechanical force. However, this force subjects the components to deformations and distortions. Thus, it is often difficult to adhere to the required low tolerances.